Synopsis... a cold low pressure system will be moving into the Great Basin Sunday and Monday. Strong westerly winds will develop over the mountains and deserts, and some light rain and snow showers may break out, creating wintery conditions over the mountains Sunday night through Monday night. Dry and a little warmer midweek, then cooler again next weekend with another chance for light precipitation as another cold trough moves south along the coast.

Winter Weather Advisory and Wind Advisory headlines were added to the forecast for the upcoming cold winter storm. The low clouds were removed from the forecast for this evening although we will probably see some scattered low clouds develop by Sunday morning. No other significant changes were made to the forecast this evening. Otherwise the previous forecast discussion remains valid below.

..previous forecast discussion...

Our string of exceptional winter weather is about to come to an end as the atmosphere undergoes an adjustment favoring troughing over the west. Monday could be the coolest day over a good chunk of the County Warning Area since last winter. A large, cold, low pressure trough will drop into the Great Basin through Monday. It will drop sfc pressure over the interior west, and force strong onshore flow across socal. Winds will be strongest over the mts. Deserts, and coastal waters. Wind and winter weather products may be needed for the mts/deserts as well as the coastal waters for the Sunday afternoon through Monday evening period.

Some light precip will break out over and west of the mts as well, and even though amounts will be limited, low snow-levels may create an impact to travelers through the mtn passes and at resort levels, especially later Mon/Mon night when the snow level will fall below 3000 feet in some areas. Up to a few inches of snow could accumulate in some spots above 4500 feet by Tue morning, but the main impact will be low windchills.

It will be much cooler through Tuesday. Maximum daytime temperatures on Monday may not get out of the 50s west of the mts, 30s at mtn resorts, and 40s over the high deserts. This equates to widespread maximum daytime temps of from 8 to 15 degrees below average.

Some moderation in temperatures will occur during the midweek period, but continued troughing over the west will keep them below average for this time of year. Generally, the European model (ecmwf) model has handled the transition to lower heights/thickness over the west better than the GFS operational runs. If we follow the latest 12z run into next weekend, it looks like another cold trough could drop south over the west with another chance of light precip and well below average temps.

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Aviation... 180500z...areas of stratus/fog will likely reach the coast between 12z and 15z sun. Cloud bases will initially be low, 600 feet mean sea level or less, but will rise rapidly around 15z sun. The initial low bases could affect ksan, kcrq and ksna. Areas of vis below 3 miles will likely occur over higher coastal terrain 12z-15z sun, but mostly improve after 15z sun. Otherwise, occasional high clouds above 20000 ft mean sea level will continue through Sunday. Clouds will increase rapidly Sunday evening from the mountains west to the coast, with bases mostly 2000-3000 ft mean sea level with higher terrain obscured, and rain showers could develop late Sunday night.

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Marine... no hazardous weather is expected through Sunday. West-northwest winds will increase to 20-35 kt late Sunday night and continue through Monday night with local gusts to 40 kt possible in the outer waters Monday morning. A gale watch has been issued for the outer waters 10 PM Sunday through 6 am Tuesday where highest winds will occur, with a Small Craft Advisory in the inner waters for the same period. Combined seas of 7-13 ft with steep waves are likely Sunday night through early Tuesday. Conditions will improve Tuesday.